This invention relates to an internal combustion engine incorporating exhaust gas recirculation and more particularly to an improvement in such an engine and in the method of operating it.
Recently, it has been proposed to improve the combustion efficiency, fuel economy, exhaust emission control and engine running at idle and low loads by introducing a substantial proportion of the intake charge under these running conditions through a relatively small cross sectional area auxiliary induction system. As a result, the induced charge enters the chambers at a high velocity to generate turbulence which improves flame propagation and the aforenoted engine running characteristics. It has also been known that the emission of nitrous oxide in the engine exhaust gases may be effectively controlled through the use of an exhaust gas recirculation (EGR) system. Most conventional engines are extremely sensitive to the amount of exhaust gas recirculation and poor running characteristics, particularly at low speeds are encountered with conventional engines using exhaust gas recirculation. It has been found that the use of the auxiliary induction system affords a greater EGR tolerance and furthermore simplifies the spark timing of an engine due to the offsetting acceleration of flame propagation by the use of the auxiliary induction system and the retardation of the rate of flame propagation through the use of exhaust gas recirculation. A problem exists, however, in accurately controlling the spark timing, exhaust gas recirculation control and the control of the proportion of the charge entering the chambers through the main and auxiliary induction systems.
It is, therefore, a principal object of this invention so as to provide an improved internal combustion engine and method of operating it that controls exhaust gas emissions, simplifies spark timing and provides good running characteristics and efficiency.
In accordance with the features aforedescribed, it has further been discovered that the aforenoted running conditions can be significantly improved by providing an enrichened fuel-air mixture during the time when exhaust gas recirculation is being accomplished. It is, therefore, a still further object of this invention to provide an improved system and method by which this may be accomplished.